1. Field of the Invention
The present invention generally relates to a semiconductor memory device, and more specifically concerns a memory device capable of being tested by an external tester or a Built-In Self Test (hereinafter, referred to as “BIST”) and including a Built-In Self Repair (hereinafter, referred to as “BISR”).
2. Description of the Related Art
In general, memory chip manufacturers perform a test on a memory at a manufacturing site.
Users depend on reliability of a chip to perform a proper operation of their system.
As a density and a linewidth of a memory cell in a memory chip are continuously reduced (currently, 0.5 micron or less), it is difficult to achieve a desired reliability.
As a result, the object of the memory device manufacturers is to increase memory capacity without reduction of chip yield due to a mis-operation product.
Before shipment of memory chips, the memory chips are tested to verify whether each memory cell of a memory array is properly performed.
In a conventional memory chip manufacturing site, memory chips have been tested by an external tester or automatic test equipment (ATE) However, it is difficult to detect a defective memory cell at a user site. Although the test equipment is usable by users, repair cost is expensive, it takes much time, and the equipment is impractical.
Thus, other memory chips comprises a BIST circuit and a BISR circuit.
When a power source is powered-up in the memory chip, the BIST is operated by a memory for reading and writing various patterns to determine a failed memory cell.
The BISR circuit repairs a row or a column which includes a failed cell with a spare row or a spare column in a memory array. As a result, normal chip performance can be obtained even when not all cells can be used because the BIST circuit and the BISR circuit are operated whenever a power source is applied to a system to detect a potential failure before the next system power source is applied.
However, since the conventional BIST and BISR performs an unconditional operation whenever a power source is applied to the system, a test by an external tester and a repair operation are performed at the same time. As a result, it is impossible to perform a precise test and an accurate repair operation.